The invention relates to a method and an apparatus for the optical surveying of a surface of a measured object by means of an image-recording system.
When taking images of a measured object by means of an image recording system, in particular when surveying the object, measures preventing a blurring of the captured image must be taken. If there is a continuous motion between the measured object and the image recording system, it is possible to use flash illumination in order to produce snapshots of the object. However, already at relatively slow speeds of, for example, 10 mm/sec and exposure times of 1/5000 sec, it is no longer possible to perform exact measuring tasks. The relative movement for the duration of the flash is already two micrometers or, with current cameras, approximately four pixels, so that the image is correspondingly blurred. In addition, there are strong light reflections when the object is illuminated with stroboscopic flash that result in the corruption of the captured image. Consequently, it is necessary to either work with very low relative speeds between the measured object and the image recording system, or with an incremental movement.
This relative movement between the measured object and the image recording system is particularly disruptive when interferometric measurements are taken. On the other hand, the principle of interferometric measurement offers a broad spectrum of options for use that should be exploited, if possible.
Document DE 10 2004 047 928 A1 discloses an optical 3D measuring process that works with a lens with a short depth of field. The lens defines a focal plane that is moved along the optical axis of the measuring system (in Z-direction) during the measuring operation. As a result of this, a series of images is recorded, this being referred to as ‘ImagestackA’. In the simplest case, this image stack is recorded with the focal plane at rest, in that the movement of the focal plane relative to the surface of the object is stopped during the measurement for image capture. Alternatively, work is done with a moving focal plane, whereby the movement speed of the focal plane relative to the image recording speed is slow. In order to increase the image recording speed, the movement of the focal plane is taken into consideration during image capture.